Impulse lightning arresters and pulse arrester columns for power lines

ABSTRACT

The inventive spark arrester comprises an odd number of series-connected spark units forming a chain, with each spark units comprising at least one discharge gap. In order to increase the reliability of protection of electric installation components having a flat voltage—time characteristic by ensuring a low discharge level and a fast response of the arrester, the output of each even spark unit is connected via a resistor to a clamp connecting the arrester to the protected components subjected to a high potential, while the output of each odd spark unit, except the last one, is connected via another resistor to another clamp connecting the arrester to the protected components subjected to a low potential. Preferred embodiments of the arrester promote a generation of a long surface discharge along a surface of tubular body made of a solid dielectric, said body being common for all spark units constituting the arrester. Arresters comprising several tubular bodies and arrester assemblies made of several arresters are also disclosed.

REFERENCE TO PRIOR APPLICATION

Thus application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in PCT patent applicationNo. PCT/RU01/00258 filed on 26 Jun. 2001 and Russian Application No.2000116337 filed 27 Jun. 2000.

FIELD OF INVENTION

The present invention relates to the field of high-voltage techniques,more precisely, to impulse lightning arresters for protecting componentsof power transmission lines and high-voltage installations againstovervoltages during a thunderstorm, said arresters consisting ofseries-connected spark gaps assembled into a chain of N (N=odd numberequal to or eater than 3) series-connected spark units (or modules). Theinvention also relates to arrester assemblies (or columns) consisting ofseveral arresters of the described type.

BACKGROUND OF THE INVENTION

Widely used prior art spark lightning arresters comprise a plurality ofspark gaps (also called discharge gaps), each gap consisting of a pairof electrodes (a typical spark gap design is described, for example, inHigh Voltage Equipment, ed. by D. V. Razevig, 1976, Energy Publishers,Moscow, p. 297, FIG. 16-10). Examples of lightning arresters comprisingseveral spark gaps are given on page 299 of said book and in RussianPatent No. 2,096,882 owned by the assignee of the present application.In case a large number of spark gaps are used, said gaps can be groupedinto spark units, with some of said units comprising greater than onespark gaps (as shown in FIG. 16-13 of the above-cited book).

For lighting protection of high-voltage electric equipment, arresterassemblies consisting of series-connected arresters of a lower voltageclass are also used (as described, for example, in High VoltageEquipment, ed. by D. V. Razevig, 1976, Energy Publishers, Moscow, p.301, FIG. 16-14).

Arresters comprising a chain of spark units and arrester assembliesprovide a long flashover path; therefore their use prevents lightningflashover from developing into a power arc, so that the electricinstallation protected by such arrester or such assembly continuesuninterrupted operation. However, as the spark units are connected inseries, a lightning overvoltage applied to the arrester is distributedamong its spark units. As a result, the arrester's discharge voltage ison the whole much higher than that of one individual spark unit, and forthat reason it is often difficult to ensure a desired low level ofovervoltage limitation.

In a impulse mode, the voltage distribution among the spark units isdetermined by their own capacities and by their capacities relative toearth. In other words, the arrester comprising series-connected sparkunits constitutes a capacitive chain. Surge voltage is very unevenlydistributed over such a chain, which results in a cascade break-down ofall the spark units, with a sequential break-down of each of dischargegaps of the individual units.

An example of the cascade lightning arrester is an impulse sparklightning arrester comprising a first clamp and a second clamp forconnecting the arrester to components of a power transmission line or anelectric installation, which clamps are under a high and low potential,respectively; and a chain of N series-connected spark units, eachcomprising a discharge gap formed by a first electrode and a secondelectrode electrically connected to the input and output of said sparkunit. The input of the first spark unit and the output of the Nth sparkunit are connected to the first and the second clamp, respectively (seeHigh Voltage Equipment, ed. by D. V. Razevig, 1976, Energy Publishers,Moscow, p. 303, FIG. 16-16).

A time front of lightning overvoltage impulse has duration of about 1 μs(microsecond), which is equivalent to the frequency f of alternatingvoltage of approximately 200 kHz. For such a high frequency, theresistance x_(C) of an additional shunt capacitor C is quite small,since this resistance is inverse to the impulse frequency: x_(C)=½πfC.As an example, for C=200 pF, the resistance of the shunt capacitor isabout 4 kOhms. Therefore, due to the presence of the additionalcapacitor, the second electrode of the discharge gap of the first sparkunit becomes connected to the ground via a relatively small resistance.Thus, voltage applied to the chain of spark units becomes appliedpractically entirely to the first gap alone. Meanwhile, other sparkunits in the chain are not subjected to any voltage. Under the impact ofthe applied voltage, the discharge gap of the first spark unit breaksdown, and the entire voltage, due to the presence of the second shuntcapacitor, becomes now applied to the second spark unit, and so on.Therefore, the arrester's triggering under application of a low voltageis ensured. However, the described cascade scheme, based on thesequential response of the spark units forming the chain, results inthat the total response time of the arrester T becomes equal to the sumof response times t of all N single spark units: T=t₁+t₂+ . . . +t_(n),that is a substantial increase of said response time takes place.

As a consequence, the voltage—time characteristic of the prior artarrester in the domain of fast response times (about 1 μs) is quitesteep, and this prevents the use of said arrester for protection offacilities with a flat voltage—time characteristic, such as cable linksor transformers, when they are exposed to steep overvoltage impulses,since the arrester's response time is long enough for the impactovervoltage to grow to values dangerous to the insulation of theprotected facility.

After the lightning impulse is over, the spark unit chain, due to theflashover of all spark units, remains exposed to an industrial voltageof 50 Hz frequency. At this stage, an even distribution of voltage overall the spark units is advantageous for more efficient extinction of anelectric arc resulting from a follow-up current in each unit. However,at 50 Hz frequency, the resistances of the additional capacitances C arerather large, so they do not have a notable effect on the voltagedistribution over the spark units.

Another example of a cascade spark arrester is the impulse sparkarrester for overvoltage protection according to SU 1,669,026. Anarrester disclosed therein comprises a first clamp and a second clampfor connecting the arrester to components of a power transmission lineor of an electric installation, which clamps are under a high and lowpotential, respectively; and a chain of N (N=odd number equal to orgreater than 3) series-connected spark units. Each unit comprises atleast one discharge gap formed by a first main electrode and a secondmain electrode, which electrodes being electrically connected to aninput and an output, respectively, of said spark unit, the input of thefirst spark unit and the output of the Nth spark unit being connected tothe first and the second clamps, respectively. The prior art arresterfurther comprises N−1 resistors, the output of each odd spark unit,except the last one, being connected to the second clamp via one of saidresistors, while the output of each even spark unit is connected to thefirst clamp via another of said resistors. This arrester, which has somefeatures in common with the arrester of the present invention,essentially solves the problem connected to the cascade break-down.Nevertheless, there still remains a need for improvements in the designof the arresters of this type.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide a reliablelightning arrester for protecting high-voltage installations againstlightning overvoltage.

Another object is to provide assemblies of electrically connectedimpulse spark lightning arresters to protect components of power linesor electric installations.

To achieve the above-stated objects, an impulse spark lightning arresterfor protecting components of power lines or electric installations isproposed. The arrester of the invention, similar to the above-describedprior art one, comprises a first clamp and a second clamp for connectingthe arrester to components of a power transmission line or of anelectric installation, subjected to a higher and a lower potential,respectively; and a chain of N (N=odd number equal to or greater than 3)series-connected spark units. Each unit comprises at least one dischargegap formed by a first main electrode and a second main electrode, saidelectrodes being electrically connected to the input and output,respectively, of said spark unit, the input of a first spark unit andthe output of a Nth spark unit being connected to the first and thesecond clamp, respectively. The arrester of the invention furthercomprises N−1 resistors, the output of each odd spark unit, except thelast one, being connected to the second clamp via one of said resistors,while the output of each even spark unit is connected to the first clampvia another of said resistors.

A main distinctive feature of the claimed arrester consist in that theresistance of each Kth (K=1, 2, . . . N−1) resistor meets one of thefollowing conditions:R_(K)>R_(K+2) for an odd K,R_(K)<R_(K+2) for an even K.

The following features may be indicated as essential for some or all ofthe preferred embodiments of the arrester.

The resistors are made of a nonlinear semiconductive material, whichfeature facilitates ensuring required resistance values for saidresistors.

At least one of the spark units (preferably each unit) additionallycomprises a body made of a solid dielectric, with the first and thesecond main electrodes mounted on a surface of said body so as to enablea generation of a surface discharge between said electrodes. Thedevelopment area of such discharge is preferably filled with fineinsulation material (such as quartz sand). In case the surface dischargeis employed, it is also desirable to place the arrester inside aninsulating sheath and to provide the arrester with at least onenonlinear resistor connected between one of the clamps and its adjacentspark unit, in order to route a surface discharge current to saidnonlinear resistor.

In one of the preferred embodiments of the impulse arresters of thepresent invention the solid dielectric body has a shape of an elongatedcup, with the first and the second main electrodes arranged at its ends.In this case an additional electrode shall be arranged inside said bodyover its entire length. The additional electrode shall be electricallyconnected to the second electrode and insulated from the firstelectrode.

In some of preferred embodiments of the arrester, the solid dielectricbody is common for all spark units, each of said units being arrangedfor generating a surface discharge between the first main electrode andthe second main electrode. The resistors in this case may be locatedinside said common solid body or on its outer surface.

In one of the embodiments of the impulse arrester according to thepresent invention the first clamp and the second clamp are mounted atthe opposite ends of the common solid body, while N coaxial spaced apartsheds made of a dielectric material are provided on its side surface. Onthe opposite surfaces of each fin, at its base, the first electrode andthe second electrode of one of the spark units are arranged.

In the next embodiment of the arrester, all spark units are arranged soas to enable a generation of a discharge over the inner surface of thecommon tubular body of a solid dielectric. Further, the first electrodeof the first spark unit and the second electrode of the third spark unitare mounted at the opposite ends of said tubular body. The secondelectrode of the first spark unit and the second electrode of the secondspark unit are mounted on the inner side surface of the common tubularbody. The latter two electrodes serve also as the first electrode of thesecond spark unit and the first electrode of the third spark unit,respectively, while the resistors are made of a semiconductive materialand are arranged on the outer surface of the tubular body at a certaindistance from each other. The inner cavity of said tubular body, atleast in its part adjacent to the outer surface where the flashoverdischarge is generated, is filled with fine-grained insulating material.

In still another preferred embodiment of the impulse arrester, thearrester comprises not one, but two tubular bodies made of a soliddielectric, wherein a center electrode is mounted on the outer surfaceof each of said tubular bodies, and wherein a first end electrode and asecond end electrode are mounted at the ends of each solid body.Further, the second end electrode and the center electrode of the firsttubular body are electrically connected to the center electrode and thefirst end electrode, respectively, of the second tubular body. In thisarrangement, the first and the second main electrodes of the first sparkunit are formed by the first end electrode and the center electrode,respectively, of the first tubular body, said spark unit comprising apart of this tubular body located between said electrodes. The first andthe second main electrodes of the second spark unit are formed by theconnections of the center electrode and the second end electrode,respectively, of the first tubular body with the first end electrode andthe center electrode, respectively, of the second tubular body. Thesecond spark unit further comprises parts of said two tubular bodieslocated between said connections. Similar to the first spark unit, thefirst and the second main electrodes of the third spark unit are formedby the center electrode and the second end electrode, respectively, ofthe second tubular body, said spark unit comprising a part of the secondtubular body located between said electrodes.

The resistors in the latter embodiment of the arrester are designed asrod electrodes made of a semiconductive material, said electrodesextending inside said tubular bodies and being connected to the endelectrodes installed on that tubular body, inside of which said rodelectrodes are mounted.

In another aspect, the present invention provides an arrester assemblyof M (M being equal to, or greater than 2) electrically connected (e.g.in series) impulse spark lightning arresters for protecting componentsof power lines or electric installations. One of said arresters isprovided with a first clamp for connecting the assembly to components ofthe power line or the electric installation subjected to a highelectrical potential, while another of said arresters is provided with asecond clamp to connect the assembly to low-potential components of saidpower line or electric installation. The main distinction of theassembly according to the present invention from prior art assemblies ofthis type is that each, or at least one, of the arresters constitutingthe assembly is constituted by any of the above-described embodiments ofthe arrester according to the present invention.

According to a preferred embodiment of the proposed assembly, allarresters constituting the assembly may be similar in their design andparameters. Where both similar arresters of the assembly contain twotubular bodies each, the center electrode of the second tubular body ofthe first arrester can be connected to the first clamp of the secondarrester, while the second clamp of the first arrester can be connectedto the center electrode of the first tubular body of the secondarrester.

In another embodiment of the arrester assembly of the invention alsousing two arresters, each arrester comprising two tubular bodies, saidarresters have different characteristics. One of said arresters servesas the main arrester, i.e. determines the lightning overvoltageprotection properties, while the second, smaller arrester serves toenhance the properties of the main one. This second arrester isconnected in parallel to the second unit of the first arrester, anddischarge voltages of the first and the third spark units of the firstarrester are selected essentially similar to a discharge voltage of thesecond arrester.

Also, different types of arresters may be combined in a single assembly.For instance, one of two arresters constituting the assembly and havinga common body made of a solid dielectric can comprise, as describedabove, electrodes mounted on the inner surface of said common tubularbody and one or two nonlinear resistors installed inside the tubularbody to close a current circuit for a discharge developing in thefine-grained insulating material. The second arrester may in this casecorrespond to the above-described arrester embodiment with two tubularbodies.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described in detail in conjunctionwith the accompanying drawings, wherein:

FIG. 1 shows a simplified diagram of an impulse lightning arrestercomprising a chain of five spark units;

FIGS. 2 to 5 show alternative embodiments of the impulse lightningarrester with tubular bodies made of a solid dielectric, along which asurface discharge will develop;

FIGS. 6 to 8 show alternative embodiments of arrester assembliescomposed of impulse arresters built on the base of the arresterembodiment shown in FIG. 5.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 presents a scheme of electrical connections for an impulselightning arrester comprising a chain of N (N=5) spark units N1 to N5.To facilitate understanding, each spark unit is shown as comprising onlyone spark gap, the gaps being designated as 1′ to 5′. A first clamp 6,so-called “potential clamp” is connected to the input of the first sparkunit N1 and serves to connect the arrester (either directly, or via anintermediate component, such as another arrester) to a component (suchas a power line conductor) of a power transmission line subjected to ahigh electrical potential U. The spark units N1-N5 are connected inseries, i.e. the output of each of the spark units N1-N4 is connected tothe input of the next spark unit N2 to N5, respectively, at anappropriate point (these connection points being designated as 7 to 10).A second, or “ground” clamp 11 of the arrester connected to the outputof the last spark unit N5, i.e. to the second electrode of this unit,serves to connect the arrester (either directly, or via an intermediatecomponent) to a grounded component of the power transmission line (suchas a power transmission tower), said component having a zero potential.Correspondingly, the potential of clamp 11 is designated in FIG. 1 as 0.

The arrester is also provided with K (K=N−1=4) conducting components,constituted, according to the present invention, by resistors 12 to 15.The first resistor 12 and the third resistor 14 are connected betweenthe “ground” clamp 11 and the outputs of the odd (the first and thethird) spark units N1 and N3, respectively (at connection points 7 and9). Due to these connections, said points 7, 9 acquire the potential ofthe “ground” clamp 11. The second resistor 13 and the fourth resistor 15are connected between the “potential” clamp 6 and the outputs of theeven spark units N2 and N4, respectively (at connection points 8, 10).Hence, said points 8, 10 acquire potential U. Thus, each of the sparkunits N1 to N5 is exposed to the electric potential U.

Each spark unit comprises a first electrode 16 and a second electrode17, both electrodes 16, 17 being electrically connected respectively tothe input and the output of the corresponding spark unit. Each pair ofelectrodes 16, 17 forms a discharge gap where a spark channel betweensaid electrodes is formed whenever an overvoltage of sufficientmagnitude occurs.

The above-described embodiment of the impulse lightning arrester of theinvention operates as follows.

Whenever a lightning overvoltage occurs, its full potential U will beapplied to each spark gap 1′ to 5′ simultaneously, due to a presence ofthe resistors 12 to 15 connected as described above. Under the impact ofthe overvoltage, a discharge develops between electrodes 16 and 17 ofall spark gaps 1′ to 5′, which results in break-down of the spark gapsof all spark units N1 to N5. In this way an electric path of a very lowresistance (about several Ohms) is created for the surge current due tolightning flowing from a high-voltage component (such as the power lineconductor) to the ground. The voltage drop in the thus created commonpath due to the flashover of the spark units chain is rather low.Therefore an impact of the lightning overvoltage on the protected powertransmission component is limited to an allowable level.

Owing to the arc-suppressing properties of the spark gaps formed betweenelectrodes 16 and 17, the follow-up arc current will be quenched as soonas the lightning surge current has passed, so that the powertransmission component protected by the arrester will continue itsuninterrupted operation.

Due to the statistical nature of the spark discharge development,non-simultaneous flashover of the spark units is possible even with thefull overvoltage potential applied to each spark unit. To ensure a fastresponse of all spark units under such circumstances, it is preferableto ensure a certain relationship, or correlation between resistances ofthe resistors 12 (R₁) and 14 (R₃), as well as those of the resistors 13(R₂) and 15 (R₄).

For example, if spark unit N1 is the first to respond, the dischargecurrent will flow from clamp 6 via said unit, then via resistor 12 (R₁)to the “ground” clamp 11 and therefrom to the ground. The resistance ofthe flashover path between main electrodes 16 and 17 is very low (a fewOhms); therefore, virtually all the voltage drop U will become appliedto resistor 12 (R₁). Therefore, resistor 12 (R₁) must in this case havea sufficiently high value (several hundred Ohms), in order to, first,restrict the current flowing through the first spark unit N1, andsecond, to ensure a voltage drop on said resistor that is sufficientlyhigh to enable the response of other spark units N2-N5.

If both spark units N1 and N3 are the first to respond, current runsthrough them and through the respective resistors 12, 14, so that avoltage drop equal to the difference of voltage drops on the resistor 12(having the resistance R₁) and the resistor 14 (having the resistanceR₃) is now applied to the spark unit N2. For the spark unit to respond,the voltage drop on the resistor 14 has to be less than the voltage dropon the resistor 12. Therefore, the resistance R₁ has to be higher thanthe resistance R₃.

A similar relation between the resistances R₂ and R₄ shall exist for theresistors 13 and 15.

In a general case, it is advantageous to select resistance values R foremployed resistors in accordance with the following relationships:R_(K)>R_(K+2) for any odd K,R_(K)<R_(K+2) for any even K,where K is a resistor number.

It should be noted that in the arrester according to the inventionnon-simultaneity in responses of the spark units is determined only by astatistical nature of a gap response characteristic (for example, bystatistics of free electrons appearance in discharge gaps).Consequently, the response time of the arrester is much shorter thanthat of the prior art arrester having the total time of the responseequal to a sum of response times of all individual spark gaps includedinto said arrester.

FIG. 2 shows, in a simplified form, a first embodiment of the impulselightning arrester according to the present invention. In thisembodiment the arrester comprises three spark units 1 to 3 ensuring adevelopment of a surface discharge at very low values of lightningovervoltage.

Each of spark units 1, 2, 3 has a tubular insulator body of a soliddielectric shaped as an extended cup 18 with a bell-shaped end, at whichend the first electrode 16 is installed. The second electrode 17 islocated on the outer surface of the opposite end of cup 18. On the innersurface of insulator cup 18 an additional electrode 19 is installed,which is electrically connected to the second electrode 17 and isolatedfrom the first electrode 16. The first electrode 16, (i.e. the input) offirst spark unit 1 is connected to the “potential” clamp 6; the secondelectrode 173 (i.e. the output) of the third, and last, spark unit 3 isconnected to the “ground” clamp 11.

Additional electrode 19 provided in each spark unit and connected tosecond main electrode 17 ensures high electric field strength at thefirst main electrode 16 when an overvoltage occurs. Moreover, additionalelectrode 19 enables development of surface discharge 20 in each of thespark units 1 to 3, i.e. of a surface discharge with a conductingsubstrate provided on another surface of the insulator body. These twofactors ensure quite low discharge voltages, which is a notableadvantage of this embodiment of the arrester.

The arrester is provided with two resistors 12, 15. The first resistor12 is connected between the “ground” clamp 11 and the output of thefirst (odd) spark unit 1, respectively (at point 7). The second resistor15 is connected between the “potential” clamp 6 and the output of thesecond (even) unit 2 (at point 8). Due to this, points 7 and 8 acquirepotentials of the “zero” and “potential” clamp 6, 11, respectively.Thus, each of spark units 1-3 becomes exposed to the voltage drop U.

FIG. 3 presents another embodiment of the arrester having N spark units,with N again being equal to 3. Unlike the previous embodiment, the oneof FIG. 3 has a single cylinder-shaped body 18 a of a solid dielectric,which body is common for all spark units 1 to 3. Located at the oppositeends of said body are the first, “potential” clamp 6 and the second,“ground” clamp 11, while its side surface has N (i.e. three) coaxialsheds 21 made of a dielectric material, such as porcelain, and mutuallyspaced apart along the axis of the body 18 a, preferably by similardistances. On the top surfaces of the three sheds 21, at their bases,first electrodes 16 of the three spark units 1 to 3 are arranged. On theopposite (bottom) surfaces of the three sheds 21 second electrodes 17 ofspark units 1 to 3 are arranged in a similar way. As in the previousembodiment, the input of the first spark unit 1 (i.e. its firstelectrode 16 ₁) and the output (the second electrode 17 ₃) of the lastspark unit 3 are connected to the first and the second clamps 6, 11,respectively.

The arrester embodiment presented in FIG. 3 comprises also K (K=N−1=2)resistors 12, 15 connected in the similar way as in the previousembodiment of the arrester (see FIG. 2). In the embodiment of FIG. 3,however, the resistors are located inside the solid body 18 a and arepreferably made of a semiconductive material in order to ensure therequired resistance value of about several hundred Ohms.

Under the impact of the overvoltage U of a sufficient magnitude,surface. discharges 20 develop over the surfaces of the sheds 21 in thespark units 1, 2 and 3. After the flashover of all spark units takesplace, the “potential” clamp 6 and the “ground” clamp 7 of the arresterbecome connected via a common path 20 of the discharge. Due to a ratherlarge length of the path 20, it quickly cools down after the passinglightning surge current, and no power arc current resulting from theapplied power-frequency voltage appears.

A pilot model of the arrester presented in FIG. 3 was tested. Said modelwas made of polyamide and had the following main dimensions:

diameter of tubular body 18a 30 mm diameter of sheds 21 80 mm thicknessof sheds 21 3 mm resistance of resistors 12, 15 9 kOhms.

The test was conducted under the impact of a standard lightningovervoltage impulse of 1.2/50 μs. Without the resistors 12 and 15ensuring a distribution of the voltage drop among the spark units, thearrester's discharge voltage was about 80 kV. With the resistors 12 and15 in place, the discharge voltage equaled 36 kV, i.e. it was abouttwice as low. Thus, it was experimentally shown that with the use of thearrester according to the described embodiment of the invention, thedischarge voltage of the arrester, starting from which its protectiveaction takes place, can be significantly reduced.

FIG. 4 presents still another embodiment of the arrester of the presentinvention, according to which the main electrodes 16, 17 of all threespark units 1, 2, 3 are arranged inside the common tubular insulatorbody 18 a. The first, “potential” clamp 6 and the second, “ground” clamp11 are respectively arranged at the top and at the bottom ends of thetubular body 18 a.

The first electrode 16 ₁ of the first spark unit 1 is located inside thetubular insulator body 18 a, at its end, and is connected to the“potential” clamp 6, which is under potential U, and to an additionalelectrode 22 a (which also serves as the resistor 15). The electrode 22a is mounted on the outer surface of the tubular body 18 a (or, as shownin FIG. 4, in a groove formed in the outer surface of the tubular body18 a).

The second electrode 17 ₁ of the first spark unit 1 is located at adistance from the first electrode 16 ₁, said distance corresponding toapproximately one third of a length of the tubular body 18 a. Thiselectrode 17 ₁ is connected to the “ground” clamp 11 via an additionalelectrode 22 b made of a semiconductive material and serving also as theresistor 12.

The second electrode 17 ₁ of the first spark unit 1 servessimultaneously as the first electrode 16 ₂ of the second spark unit 2.The second main electrode 17 ₂ of the second spark unit 2 is located ata distance of approximately one-third of the length of the tubular body18 a from the first electrode 16 ₂ of said unit and is connected to theresistor 15 serving to supply the potential U from the “potential” clamp6 to the first electrode 16 ₃ of the third spark unit 3.

The third spark unit 3 is designed similar to the spark unit 1 asdescribed above, that is it comprises the first main electrode 16 ₃ andthe second main electrode 17 ₃ located at a distance therefrom, insidethe tubular insulator body 18 a, near its bottom end, and connected tothe “ground” clamp 11 staying under zero potential.

The inner space of the tubular body 18 a is filled with fine-grainedinsulating material 22, such as quartz sand (QS).

To improve the performances of the arrester, it may be provided with atleast one nonlinear component 23 arranged inside the tubular body 18 aand included into the current circuit. Under the impact of a lightningovervoltage, a path of the surface discharge 20 develops along the innersurface of the tubular body 18 a in spark unit 1. Development of thisdischarge is promoted by additional electrodes 22 a and 22 b (this roleof the additional electrodes is illustrated in FIG. 4 by the fact thatin the first and the third spark units 1, 3 the creeping dischargedevelops on that side of the tubular body 18 a, which is adjoined by theadditional electrode 22; while in the second spark unit 2 interactingwith both additional electrodes the creeping discharge can, with similarprobability, develop on both sides of the tubular body).

Filling of the cavity of the tubular body 18 a with a fine-grainedinsulator material ensures efficient quenching of the follow-up arccurrent. During the passage of a lightning overvoltage impulse, thenonlinear component 23 has a low resistance, and when the lightningimpulse is over, its resistance rises sharply and the follow-up arccurrent strength is restricted, which promotes efficient arc quenchingin the spark gaps. The combination of efficient arc quenching andcompact design is the main advantage of the arrester embodiment shown inFIG. 4.

FIG. 5 presents still another embodiment of the impulse lightningarrester, also having three spark units 1, 2, 3 formed, in contrast withthe previous embodiments, with the use of two tubular bodies 18 ₁, 18 ₂made of the solid dielectric. A center electrode 24 ₁, 24 ₂ is installedon the outer surface of each tubular body 18 ₁, 18 ₂ in its middle part;a first end electrodes 25 ₁, 25 ₂ are installed at the top end of eachtubular body, and a second end electrodes 26 ₁, 26 ₂, are installed atits bottom end. Furthermore, as it is shown in FIG. 5, the first endelectrode 25 ₁ of the first tubular body 18 ₁ and the second endelectrode 26 ₂ of the second tubular body are connected to the first,“potential” clamp 6 of the arrester and to the second, “ground” clamp11, respectively. The second end electrode 26 ₁ and the center electrode24 ₁ of the first tubular body 18 ₁ are electrically connected to thecenter electrode 24 ₂ of the second tubular body 18 ₂ and to its firstend electrode 25 ₂, respectively.

Thus, in this embodiment of the arrester, the first spark unit 1 isformed by the first end electrode 25 ₁ and by the center electrode 24 ₁of the first tubular body 18 ₁ (said electrodes 25 ₁ and 24 ₁ serving asthe first electrode 16 ₁ and the second electrode 17 ₁) and by a part ofsaid tubular body confined between the electrodes 25 ₁ and 24 ₁.

The first main electrode 16 ₂ of the second spark unit 2 is formed byconnecting center electrode 24 ₁ of the first tubular body 18 ₁ to thefirst end electrode 25 ₂ of the second tubular body 18 ₂; the secondmain electrode 17 ₂ of that unit is formed by connections of the secondend electrode 26 ₁ of the first tubular body 18 ₁ to the centerelectrode 24 ₂ of the second tubular body 18 ₂. In this case, said sparkunit 2 contains also those parts of both tubular bodies, which areconfined between said connections.

The design of the third spark unit 3 is similar to the design of unit 1:it is formed by the center electrode 24 ₂ and the second end electrode26 ₂ of the second tubular body 18 ₂ (which electrodes serve as thefirst main electrode 16 ₃ and the second main electrode 17 ₃,respectively) and a part of said tubular body confined between saidelectrodes.

The functions of the resistors 15 and 12 connecting the second electrode17 ₁ of the first spark unit and the second electrode 17 ₂ of the secondspark unit to the “zero” and “potential” clamps 11, 6, respectively, areperformed by additional rod electrodes 21 ₂ and 21 ₁ installed insidethe second tubular body 18 ₂ and the first tubular body 18 ₁.

Thus, this embodiment of the arrester also provides, for all three sparkunits 1, 2, 3, conditions necessary for simultaneous development of thesurface discharges 20 between the respective main electrodes of eachunit. These surface discharges 20 generate a long common flashover pathas a result of the break-down of all spark units following a lightningovervoltage.

As was mentioned above, a distinctive feature of this embodiment is theuse of two tubular bodies 18 ₁ and 18 ₂, due to which use the dischargegap of the second spark unit is formed not by two, but by fourelectrodes 24 ₁-25 ₂ and 26 ₁-24 ₂ connected in pairs. Furthermore, thedistance between the tubular bodies and their relative orientation maybe adjusted to suit specific design requirements for the arrester and/orspecific conditions of its application.

An advantage of this embodiment (as well as the previous one) of thearrester is combining by components 21 ₁ and 21 ₂ the functions ofadditional electrodes promoting development of the surface discharge andresistors providing the required potential distribution in accordancewith the present invention.

The serviceability and efficiency of the embodiment presented in FIG. 5when applied to arresters of the 10 kV class was experimentally tested.The test model of the arrester was made using two lengths of cable witha semiconductive polyethylene core performing the functions of resistorsand additional electrodes. The core diameter was 10 mm, and theresistance of each resistor was 400 Ohms. The tubular bodies were formedby insulating said cable lengths with high-pressure polyethylene. Thetubular body wall thickness was 3 mm. The length of each spark unit 1,2, 3 was about 27 cm. Thus, the overall flashover length was about 80cm. The discharge voltage of the arrester under the impact of a standardlightning impulse (1.2/50 μs) was 80 kV. It should be noted that with achain of three spark units of a similar design, but without theresistors enforcing potential distribution among the electrodes, thedischarge voltage is about 150 kV, i.e. much higher.

With design characteristics properly selected, all the above-describedembodiments of the impulse lightning arrester of the invention ensurereliable response of the arrester at relatively low magnitudes oflightning overvoltages, due to the virtually simultaneous response ofall spark units, with subsequent connection of the spark units'discharge filaments into a single current path. All of the describedembodiments are easy to manufacture and reliable in operation.Furthermore, other embodiments of the present invention are alsopossible. For instance, to improve the power arc quenching efficiency,the arresters may be inserted into an insulation sheath 27 filled withfine-grained insulator material 22, such as quartz sand QS, as it isshown in relation to the arrester embodiment of FIG. 5 (the efficiencyof such solution is demonstrated in the Russian Patent No. 2,146,847owned by the assignee of the present application).

Where filling with fine insulation material is used, it is advisable, asshown in FIG. 5, to provide the arrester additionally with at least onenonlinear resistor 23 installed between one of clamps 6 (11) and theadjacent first (last) spark unit, for routing to said nonlinear resistorthe surface discharge developing in said insulation material. It ispreferable to use in this case nonlinear resistors (varistors) connectedto both clamps 6, 11.

In addition, for efficient quenching of the follow-up arc current incase of only one spark unit responding properly (which situation ispossible on very rare occasions, at relatively low overvoltagemagnitudes), it is advisable to form the resistors 12 and 15 also asnonlinear components (varistors). For example, for a 10 kV-classarrester, the nonlinear resistor 23 can be made of varistor discs with adiameter of 50 mm, and resistors 12 and 15 can be made of varistor discswith a diameter of 8 mm. If the overvoltage just slightly exceeds thearrester's response voltage, a flashover can have place only in onespark unit, for example, in the spark unit 1 (see FIG. 5). In such casethe lightning surge current flows from the clamp 6 via the nonlinearresistor 23, via the first electrode 16 ₁, of the first spark unit, viathe lightning flashover path 20, via the second electrode 17 ₁ of thefirst spark unit, and further via the first electrode 16 ₂ of the secondspark unit, the resistor 12 made of varistors, the second electrode 17 ₃of the third spark unit, the nonlinear resistor 23, the clamp 11, andfurther to the ground. It may be seen that in this case the nonlinearresistor 12 is included into the discharge circuit; so that after thelightning surge current impulse has passed, said resistor sharplyincreases its resistance and prevents generation of arc current at 50 Hzfrequency.

As has been noted above, in a number of practical cases, for examplewhen high-voltage arresters are unavailable, an arrester assembly may beused instead of a single arrester. Such arrester assembly consists oftwo or more electrically interconnected arresters of a lower voltageclass. Any modifications of the arrester according to the invention canbe used as components of the arrester assembly. As an illustration, FIG.6 presents an embodiment of the arrester assembly comprising twoarresters similar to that presented in FIG. 5. In this embodiment thearresters are connected in series. This means that a first clamp 6-1 ofa first arrester 28 serves for connecting the assembly to components ofa power transmission line or of an electric installation subjected to ahigh electrical potential U; a second clamp 11-2 of a second arrester 29is intended to connect the assembly to low-potential components of thepower transmission line or of the electric installation; while a secondclamp 11-1 of the first arrester 28 is connected to a first clamp 6-2 ofthe second arrester 29.

If the arrester embodiment with two tubular bodies is employed, a novelapproach to building the arrester assembly consisting of two or morearresters may be used, as illustrated by FIG. 7. In the presentedembodiment, the functions of the clamps 6-1 and 11-2 are similar to thefunctions of the similar clamps in the above-described embodiment of theassembly. However, in this case, a center electrode 24 ₂ of a secondtubular body 18 ₂ of the first arrester 28 is connected to the firstclamp 6-2 of the second arrester 29, while the second clamp 11-1 of thefirst arrester is connected to a center electrode 24 ₁ of the firsttubular body 18 ₁ of the second arrester 29. It is evident that withsuch connection scheme of arresters 28, 29, high potential U is suppliedvia a rod electrode (resistor) 21 ₁ of the first tubular body 18 ₁ and acenter electrode 24 ₂ of the second tubular body of the first arrester28 to a first end electrode 25 ₁ of the first tubular body 18 ₁ of thesecond arrester 29. The same high potential U is further supplied via arod electrode (resistor) 21 ₁ of the first tubular body 18 ₁ of thesecond arrester 29 to a center electrode 24 ₂ of the second tubular body18 ₂ of the second arrester 29.

The low potential 0 is supplied via a rod electrode (resistor) 21 ₂ ofthe second tubular body 18 ₂ and a center electrode 24 ₁ of the firsttubular body 18 ₁ of the second arrester 29 to a second end electrode 26₂ of the second tubular body 18 ₂ of the first arrester 28, and isfurther supplied via the rod electrode (resistor) 21 ₂ of the secondtubular body 20 ₂ of the first arrester 28 to the center electrode 24 ₁of the first tubular body 18 ₁ of the first arrester 28.

Thus, the same voltage drop U-0 equal to the effective overvoltage U issimultaneously applied to all spark units of the first andsecond-arresters of the arrester assembly. Due to this, the response ofthe individual spark units and of the entire arrester assembly is fastand virtually simultaneous, which ensures better technical performanceof the inventive arrester assembly compared to prior art ones.

It is evident that in the above-described embodiment, as in the previousones, the number of arresters forming the assembly may be increased, ifnecessary, without a limitation.

As shown by the above-described test of the arrester with two tubularbodies (shown in FIG. 5), when a lightning overvoltage impulse isapplied to an arrester with discharge gaps of equal length, the firstand the third spark unit are flashed over first, while the second sparkunit is flashed over only after a certain time interval. The sparkdischarge filaments in the first and in the third spark units developfaster than in the second spark unit, because the discharge current inthe first and in the third spark units flows only along the dischargepath and through one respective resistor, while in the second spark unitthe discharge current flows along the discharge path and through tworesistors connected in series (those of the first and the second tubularbodies). As a result, the retarding effect of the resistors on the pathdevelopment is stronger in the second spark unit.

The problem of discharge retardation in the second spark unit can besolved by using the assembly of two arresters presented in FIG. 8.Unlike the previous embodiments, it consists of arresters havingdifferent sizes.

A first, larger arrester 28 serves as the main one. By its clamps 6-1and 11-1 it is connected to protected power transmission componentshaving a high U and a low potential 0, respectively. A second, smallerarrester 29 serves as a supplementary intended to increase simultaneityof response of the spark units in the main arrester 28. The secondarrester is connected in parallel to the second spark unit 2 ₁ of thefirst arrester 28 to act as a shunt. More specifically, the first andthe second clamps 6-2, 11-2 of the second arrester are connected,respectively, to the center electrode 24 ₁ and to the second endelectrode 26 ₁ of the first tubular body 18 ₁ of the first arrester 28.Furthermore, the discharge voltages of the first and third spark units1, 3 of the first arrester 28 are selected to be similar to thedischarge voltage of the second arrester 29. As a result, the flashoverof the second arrester 29 takes place virtually simultaneously with theflashover of the spark units 1, 3 of the first arrester 28, ensuring inthis way a fast formation of a single common discharge path.Consequently, a fast response of the arrester assembly as a whole isachieved. As a result, higher performance of the assembly is attainedcompared to a single main arrester.

The embodiments of the arrester assemblies reviewed above employs onlyarresters of the same type. There are situations, however, when it isadvisable to make such assemblies from arresters of differentmodifications. For example, it has been found that in some cases, whencharacteristics of arrester components are not selected quite properlyor when there presents a scatter in their characteristics, and given aneffective overvoltage of a certain value, instead of the flashover ofall spark units of the arrester of FIG. 4, only the first spark unitthereof will respond. In this case, quenching of the arc current must beprovided taking into account that only a single spark unit had abreakdown. For this purpose, it is advisable to use an arrester assemblycomprising an arrester, in which the discharges takes place in afine-grained insulation environment (such as the arrester shown in FIG.4), which arrester is connected in series with the described arresterusing two tubular bodies.

It is obvious that subject to specific requirements set for the qualityof protection of components of power lines and/or high-voltageinstallations against lightning overvoltages, and subject toavailability of such or another modifications of arresters, it can beexpedient to use also other combinations of arresters according to thepresent invention, or of arrester assemblies built up of arrestersaccording to the present invention in combination(s) with appropriateprior art arresters.

1. An impulse spark arrester for protecting components of electric powertransmission lines or electric installations, said arrester comprising:a first clamp and a second clamp for connecting the arrester tocomponents of the power transmission line or electric installationsubjected to a higher and a lower potential, respectively; a chain of N(N being an odd number equal to or greater than 3) of series-connectedspark units, each comprising at least one discharge gap formed by afirst main electrode and a second main electrode, which electrodes beingelectrically connected to an input and an output, respectively, of acorresponding spark unit, the input of a first spark unit and the outputof a Nth spark unit being connected to the first clamp and to the secondclamp, respectively; and N−1 resistors, the output of each odd sparkunit, except the last one, being connected via one of said resistors tothe second clamp, and the output of each even spark unit being connectedvia another of said resistors to the first clamp, characterized in thatthe resistance of each Kth (K=1, 2, . . . N−1) resistor meets one of thefollowing conditions:R_(K)>R_(K+2) for an odd K,R_(K)<R_(K+2) for an even K.
 2. The impulse arrester according to claim1, characterized in that the resistors are made of a nonlinearsemiconductive material.
 3. The impulse arrester according to claim 1,characterized in that at least one of the spark units additionallycomprises a body made of a solid dielectric, with the first and thesecond main electrodes mounted on a surface of said body so as to enablea generation of a surface discharge between said electrodes.
 4. Theimpulse arrester according to claim 3, characterized in that a zone of adevelopment of said surface discharge is filled with fine-grainedinsulation material.
 5. The impulse arrester according to claim 4,characterized in that the fine-grained insulation material is quartzsand.
 6. The impulse arrester according to claim 4, characterized inthat it is placed inside an insulating sheath.
 7. The impulse arresteraccording to any of claims 2 to 6, characterized in that it isadditionally provided with at least one nonlinear resistor connectedbetween one of the clamps and the adjacent spark unit in order to routea surface discharge current to said nonlinear resistor.
 8. The impulsearrester according to any of claims 3-6, characterized in that the soliddielectric body is shaped as an elongated cup.
 9. The impulse arresteraccording to claim 8, characterized in that the first and the secondmain electrodes are arranged at the ends of the solid dielectric body,wherein an additional electrode is arranged inside the solid dielectricbody over its entire length, said additional electrode beingelectrically connected to the second electrode and insulated from thefirst electrode.
 10. The impulse arrester according to any of claims3-6, characterized in that each of the spark units is arranged forgenerating a surface discharge between the first main electrode and thesecond main electrode, wherein: said solid dielectric body is common forall said spark units; the first clamp and the second clamp are locatedat the opposite ends of said common solid body; N coaxial spaced apartsheds of a dielectric material are provided on a side surface of saidcommon solid body; the first main electrode and the second mainelectrode of one of the spark units are arranged on the oppositesurfaces of each fin, at its base; and the resistors are located insidesaid common solid body.
 11. The impulse arrester according to any ofclaims 2 to 5, characterized in that the number N of the spark units isselected to be three, wherein: all spark units are arranged so as toenable a generation of the discharge between the first main electrodeand the second main electrode over the inner surface of a tubular soliddielectric body, which body is common for all spark units; the firstelectrode of the first spark unit is mounted at one end of said commontubular body; the second electrode of the third spark unit is mounted atthe opposite end of said tubular body; the second electrode of the firstspark unit and the second electrode of the second spark unit are mountedon the inner side surface of the common tubular body and servesimultaneously as the first electrode of the second spark unit and thefirst electrode of the third spark unit, respectively; the resistors arearranged on the outer surface of the tubular body spaced apart from eachother; the output of the first, odd, spark unit is connected via one ofsaid resistors to the second clamp, while the output of the second,even, spark unit is connected via another resistor to the first clamp;and the inner cavity of the tubular body is filled with fine-grainedinsulating material, at least in a zone adjacent to a part of the outersurface, along which the flashover discharge is generated.
 12. Theimpulse arrester according to claim 11, characterized in that it isprovided with at least one nonlinear resistor installed inside saidtubular body in order to route a current of the surface dischargedeveloping in the fine insulating material to said nonlinear resistor.13. The impulse arrester according to any of claims 2 to 6,characterized in that each spark unit is designed so as to enablegeneration of a surface discharge between the first main electrode andthe second main electrode of said spark unit, wherein: the arrestercomprises two tubular bodies made of the solid dielectric, with a centerelectrode mounted on the outer surface, and a first and a second endelectrodes mounted at the ends of each of said bodies; the second endelectrode and the center electrode of the first tubular body areelectrically connected to the center electrode and the first endelectrode, respectively, of the second tubular body; the first mainelectrode and the second main electrode of the first spark unit areformed, respectively, by the first end electrode and the centerelectrode of the first tubular body, said first spark unit comprising apart of said tubular body confined between said electrodes; the firstand the second main electrodes of the second spark unit are formed,respectively, by the connections of the center electrode and the secondend electrode of the first tubular body to the first end electrode andthe center electrode, respectively, of the second tubular body, saidsecond spark unit comprising the parts of said tubular bodies locatedbetween said connections; the first main electrode and the second mainelectrode of the third spark unit are formed, respectively, by thecenter electrode and the second end electrode of the second tubularbody, said spark unit comprising the part of said second tubular bodylocated between said electrodes; the resistors are designed as rodelectrodes made of the semiconductive material, said electrodesextending inside said tubular bodies and being connected to the endelectrodes mounted on the tubular body containing said rod electrodes,the output of the first spark unit being connected via one of saidresistors to the second clamp, and the output of the second spark unitbeing connected via the other said resistor to the first clamp.
 14. Animpulse lightning spark arrester for protecting components of powertransmission lines or electric installations, said arrester comprising:a chain of N (N=odd number equal to, or greater than 3) series-connectedspark units; N−1 conducting components; and a first clamp and a secondclamp for connecting the arrester to components of the power line or theelectric installation subjected to a high and a low potential,respectively, wherein each of said spark units comprises at least onedischarge gap formed by a first main electrode and a second mainelectrode, which electrodes being electrically connected to an input andan output, respectively, of a corresponding spark unit, the input of thefirst spark unit and the output of the Nth spark unit being connected tothe first clamp and the second clamp, respectively, wherein each Kth(K=1, 2, . . . N−1) conducting component is connected between the outputof the Kth spark unit and one of the clamps, characterized in that allspark units are designed so as to enable generation of a dischargebetween the first main electrode and the second main electrode over thesurface of a solid dielectric body, whereon the first main electrode andthe second main electrode are mounted, said body being common for allthe spark units, wherein: the first and the second clamps are mounted atopposite ends of said common solid body; N coaxial spaced apart sheds ofa dielectric material are provided on a side surface of said commonsolid body; the first main electrode and the second main electrode ofone of the spark units are arranged on the opposite surfaces of eachshed, at its base; the conducting components are designed as resistorsof a semiconductive material located inside said common solid body; theoutput of each odd spark unit is connected to the second clamp via oneof said resistors, while the output of each even spark unit is connectedto the first clamp via another of said resistors.
 15. The impulselightning spark arrester according to claim 14, characterized in that azone of a development of the surface discharge is filled with fineinsulating material, preferably constituted by quartz sand, wherein: thearrester is placed inside an insulating sheath and is additionallyprovided with at least one nonlinear resistor connected between one ofthe clamps and its adjacent spark unit in order to route the surfacedischarge current developing in said material to said nonlinearresistor.
 16. An impulse lightning spark arrester for protectingcomponents of power transmission lines or electric installations, saidarrester comprising: a chain of N (N=3) series-connected spark units;N−1 conducting components; and a first clamp and a second clamp forconnecting the arrester to components of the power line or the electricinstallation subjected to a high and a low potential, respectively,wherein each of said spark units comprises at least one discharge gapformed by a first main electrode and a second main electrode, whichelectrodes being electrically connected to an input and an output,respectively, of a corresponding spark unit, the input of the firstspark unit and the output of the Nth spark unit being connected to thefirst clamp and the second clamp, respectively, wherein each Kth (K=1,2) conducting component is connected between the output of the Kth sparkunit and one of the clamps, characterized in that: all spark units aredesigned so as to enable generation of a discharge between the firstmain electrode and the second main electrode over the surface of atubular body made of a solid dielectric, said body being common for allthe spark units; the first electrode of the first spark unit is mountedat one end of said tubular body; the second electrode of the Nth sparkunit is mounted at the opposite end of said tubular body; the secondelectrode of the first spark unit and the second electrode of the secondspark unit are mounted on the inner side surface of the common tubularbody and simultaneously serve as the first electrode of the second sparkunit and the first electrode of the third spark unit, respectively; theconducting components are designed as resistors of a semiconductivematerial arranged on the outer surface of the tubular body spaced apartfrom each other; the output of the first, odd, spark unit is connectedvia one of said resistors to the second clamp, while the output of thesecond, even, spark unit is connected via another resistor to the firstclamp; and the inner cavity of the tubular body is filled withfine-grained insulating material, at least in a zone adjacent to a partof the side surface, along which the flashover discharge is generated.17. The impulse arrester according to claim 16, characterized in that itis additionally provided with at least one nonlinear resistor installedinside said tubular body in order to route a current of the surfacedischarge developing in the fine-grained insulating material to saidnonlinear resistor.
 18. An impulse lightning spark arrester forprotection of components of power transmission lines or electricinstallations, said arrester comprising: a chain of threeseries-connected spark units; two conducting components; and a firstclamp and a second clamp for connecting the arrester to components ofthe power line or the electric installation subjected to a high and alow potential, respectively, wherein each of said spark units comprisesat least one discharge gap formed by a first main electrode and a secondmain electrode, which electrodes being electrically connected to aninput and an output, respectively, of a corresponding spark unit, theinput of the first spark unit and the output of the third spark unitbeing connected to the first clamp and the second clamp, respectively,and the first and the second conducting component being connectedbetween the outputs of the first and the second spark unit and one ofthe clamps, respectively, characterized in that all the spark units aredesigned so as to enable generation of a surface discharge between thefirst main electrode and the second main electrode, wherein: thearrester comprises two tubular bodies of a solid dielectric, with acenter electrode mounted on the outer surface, and a first and a secondend electrode mounted at the ends of each of said bodies; the second endelectrode and the center electrode of the first tubular body areelectrically connected to the center electrode and the first endelectrode, respectively, of the second tubular body; the first and thesecond main electrode of the first spark unit are formed, respectively,by the first end electrode and the center electrode of the first tubularbody, said spark unit comprising a part of said first tubular bodyconfined between said electrodes; the first main electrode and thesecond main electrode of the second spark unit are formed, respectively,by the connections of the center electrode and the second end electrodeof the first tubular body to the first end electrode and the centerelectrode, respectively, of the second tubular body, said second sparkunit comprising parts of said tubular bodies located between saidconnections; the first and the second main electrode of the third sparkunit are formed, respectively, by the center electrode and the secondend electrode of the second tubular body, said third spark unitcomprising a part of said second tubular body confined between saidelectrodes; the conducting components are resistors designed as rodelectrodes made of a semiconductive material, said electrodes extendinginside said tubular bodies and being connected to the end electrodesmounted on the tubular body containing said rod electrodes; the outputof the first spark unit is connected via one of said resistors to thesecond clamp, and the output of the second spark unit is connected viathe other said resistor to the first clamp.
 19. The impulse lightningspark arrester according to claim 18, characterized in that a zone of adevelopment of the surface discharge is filled with fine insulatingmaterial, preferably constituted by quartz sand, wherein: the arresteris placed inside an insulating sheath and is additionally provided withat least one nonlinear resistor connected between one of the clamps andits adjacent spark unit, in order to route a current of the surfacedischarge developing in said material to said nonlinear resistor.
 20. Anarrester assembly consisting of M (M being equal to, or greater than 2)electrically connected impulse lightning spark arresters for protectingcomponents of power lines or electric installations, each arrestercomprising at least one spark unit, wherein one of said arresters isprovided with a first clamp to connect the assembly to components of thepower line or the electric installation subjected to a high electricalpotential, while another of said arresters is provided with a secondclamp to connect the assembly to components of the power line or theelectric installation subjected to a low electrical potential, saidassembly characterized in that at least one of said arresters isconstituted by an arrester according to any of claims 1 to
 6. 21. Theassembly according to claim 20, characterized in that all arresters ofsaid assembly are connected in series.
 22. The assembly according toclaim 20, characterized in that all arresters of said assembly aresimilar to each other.